1. Field of the Invention
The present invention generally relates to a magneto optical recording medium such as a magneto optical disc, and more particularly to a magneto optical recording medium of the so-called super resolution reproduction type to record and reproduce information by a spatial frequency higher than the spatial frequency prescribed by the light beam (i.e. the spatial frequency prescribed by the wavelength of the reading light beam and the numerical aperture of the objective lens at the time of reproduction).
2. Description of the Related Art
The magneto optical recording medium of the super resolution reproduction type is quite advantageous to increase the recording density of the information.
The magneto optical disc of this type is provided with a record layer, which carries the information by its magnetization direction, a reproduction layer, which rotates the polarization plane of the reading light beam for the reproducing operation, and an intermediate layer, which magnetically switched-connected to the record layer and the reproduction layer. In operation, the magnetization direction as the information of the record layer at only one portion within the light beam spot is transferred from the record layer to the reproduction layer by the switched connection force through the intermediate layer on the basis of the temperature distribution within the light beam spot. Namely, only the portion within the light beam spot, which may be a high temperature area, a low temperature area or a middle temperature area, allows the magnetization to be transferred by the switched connection force between those magnetic layers. In order to transfer the magnetization of the record layer to the reproduction layer, the switched connection force between those two layers through the intermediate layer should be larger than the coercive force of the reproduction layer.
However, in the practical cases, it is rather difficult to obtain a desirable switched connection force between the reproduction layer and the intermediate layer, and at the same time, obtain a desirable switched connection force between the record layer and the intermediate layer so as to obtain the practically sufficient C/N (Carrier to Noise ratio) by transferring the magnetization of the record layer to the reproduction layer through the intermediate layer only at the particular portion having a certain temperature within the light beam spot.